Devices for relieving high pressures within an over-pressurized system or vessel have been used in industry for many years. These devices, which are commonly known as rupture discs, provide a safety mechanism to relieve excess pressure from an over-pressurized system or vessel when a potentially dangerous over-pressure exists within the system. The rupture discs are typically placed within a vent or a pressure vessel of the system so as to prevent flow of fluid through the vent until an overpressure condition actually occurs. Each rupture disc is specifically designed to rupture at a pre-determined pressure and temperature thus relieving the pressure within the particular system.
Rupture discs typically include a disc dome and so called tension-type rupture discs (in contrast to so-called reverse bucking discs) are typically oriented in a particular system such that the disc dome points away from the pressure side of the vent such that pressure is applied against the concave side of the rupture disc. This means that the concave side of the disc dome faces the internal region or upstream side of the vent where pressurized fluid is likely to produce an overpressure condition. When the fluid reaches the pre-determined pressure and temperature for which the rupture disc was designed to rupture, the tensile strength of the rupture disc material is breached, and a rupture occurs.
Rupture discs are typically mounted in conjunction with at least one support structure which is positioned and located adjacent the rupture disc on the inlet or upstream side of the fluid flow entering the disc. Inlet support structures provide additional strength and rigidity to the installation configuration and such structures can be a separate member, or they can be formed integral with the rupture disc, or they can be part of an axillary component which abuts the rupture disc or is in close proximity to the rupture disc. A downstream support structure may likewise be utilized in certain situations depending upon the particular system application and the particular type of rupture disc being utilized. Both the upstream (inlet) and downstream support structures help to hold the rupture disc in place between the adjacent pipe sections.
A prior art rupture disc 1 and a conventional inlet support member 3 are illustrated in FIG. 1. Typically the rupture disc 1 is formed of a metal material which can include a number of compositions such as stainless steel, nickel, aluminum, gold, tantalum and a number of composite materials, and the support member 3 is likewise typically formed of metal, although it may also be formed from plastic or another rigid material sufficient to ensure the proper operation of the rupture disc 1. The rupture disc 1 includes an annular flat flange region 5, a transition region 6, and a disc dome 7 as would be understood by those skilled in the art. The disc dome 7, transition region 6, and the annular flat flange region 5 are preferably integrally formed. The disc dome 7 is typically semi-spherical in shape having a convex and a concave side that projects outwardly away from the annular flange 5 as illustrated in FIG. 1. The annular flat flange region 5 is typically in a circular or annular shape that surrounds the entire circumference of the disc dome 7.
Some prior art rupture disc domes such as disc dome 7 may include, for example, a deformation (not illustrated) formed at or near the geometric apex of the disc dome 7, or at other locations on the dome. These deformations are provided to weaken the integrity of the disc dome so that when pressure is applied to the dome from within an over-pressured system, it will rupture at a pressure which is lower than the rated pressure for the same rupture disc with no such deformations. These deformations may take the form of a dimple, a score line, or other weakening means so as to control the desired rupture pressure.
The prior art support member 3 includes an annular or circular flange member 8 having an inner diameter 9 and an outer diameter 11. The support member 3 is typically an annular-shaped device formed between the inner diameter 9 and the outer diameter 11 as illustrated in FIG. 1. A center aperture 13 extends through the support member 3 and is defined by the inner diameter 9. As previously explained, the support member 3 acts as a support backing or holder for helping to hold the rupture disc in proper position in a particular system and it is positioned adjacent to, and may be attached to, or even integrally formed with, the rupture disc 1. The center aperture 13 is typically designed to coincide with the inner diameter or other dimensions of the annular flat flange region 5 associated with the rupture disc 1. This means that flow area through the inlet support structure 3 will typically coincide with the flow area through the annular flange 5 of the rupture disc 1 so as not to impede or hinder the fluid flow through the rupture disc when rupture occurs. In alternative embodiments, the support member 3 may take on other shapes that complement and are compatible with an alternatively shaped rupture disc 1.
When an overpressure is detected within the vessel or chamber associated with the rupture disc 1 and the support member 3, the over-pressured fluid flows through the center aperture 13 of support member 3 and applies an outward pressure on the concave side of the disc dome 7. This fluid pressure causes the disc dome 7 to rupture at its pre-determined rupture pressure. This releases the excess pressure within the vessel or system and prevents a build-up of pressure within the system from exploding and damaging the pressure system or vessel.
FIGS. 2 and 3 illustrate the rupture disc 1 and the support member 3 after rupturing to release pressure from within the pressurized system or vessel. When the disc dome 7 ruptures, a plurality of petal-shaped fragments, or petals 15 are formed. Four petals 15 are shown in FIG. 2. The petals 15 illustrated in FIG. 2 are similar in size and shape and are symmetrically shaped. However, typically when the disc dome 7 ruptures to form the petals 15, depending on the particular pre-determined rupture pressure, the type and material used for the rupture disc, and the actual location of pressure that is applied on the disc dome 7, other shapes and sizes of petals 15 may be formed. The petals 15 themselves may be symmetrically shaped when they are formed after disc dome 7 ruptures as illustrated in FIGS. 2 and 3, but not under all circumstances. Unsymmetrically shaped petals may likewise result after rupture. Also, the presence or absence of a deformation or perforated score lines in the disc dome 7 may cause the fragments or petals 15 formed from the rupture of a disc dome to take on a different shape.
The petal fragments 15 formed after the disc dome 7 ruptures each include a base portion 17 and a tip portion 19. The base portion 17 is the portion of the petals 15 that remain attached to the annular flat flange 5 in the transition region 6 after the disc dome 7 ruptures. The base portion 17 is wider than the tip portion 19 so that the petals 15 form a triangle-like shape (though because of the rupture, that triangle is somewhat deformed) with the petals 15 narrowing from the base portion 17 to the tip portion 19.
When the disc dome 7 ruptures, a pressure relief outlet opening or aperture 21 is formed within the rupture disc 1 that extends through the support member 3. The relief outlet opening 21 provides a channel through which the over-pressured fluid may flow to relieve the pressure within its associated pressure system or vessel. The aperture 21 may take on a number of different shapes depending on the shape the fragments 15 of the disc dome 7 take on after rupturing.
When the disc dome 7 ruptures, the base portions 17 of the petals 15 are typically somewhat curved and deformed inwardly toward the center of the pressure relief aperture 21, and the tip portions 19 are typically curved and deformed outwardly away from the center of the pressure relief aperture 21. Due to the shape of the inlet support member 3 substantially overlaying the annular flange 5 of the rupture disc 1, the base portions 17 of the petals 15 are not cleanly formed when the disc dome 7 ruptures and the inner diameter edge of the aperture 13 of the support member forces the base portions 17 of the petals 15 to extend somewhat into the area defined within the pressure relief aperture 21. In addition, the base portions 17 tend to crumple or wrinkle as a result of having over pressured fluid applied thereto, and these crumpled or wrinkled portions 23 are formed at the bottom of the base portions 17 of the petals 15 and likewise extend over and into the pressure relief opening 21, all of which reduces the flow area 21 through the rupture disc as illustrated in FIGS. 2 and 3.
As excess pressure fluid flows outwardly through the pressure relief aperture 21, the crumpled sections 23 as well as base portions 17 of the petals 15 obstruct fluid flowing through the pressure relief aperture 21 and likewise cause such fluid flow to be somewhat turbulent. This also prevents the excess pressure fluid from escaping the pressure relief aperture 21 in a laminar, smooth flow, thus increasing the time it takes for the over-pressured system to release its excess pressure. In a perfect world, the maximum flow area through the pressure relief aperture 21 would be equal to the flow area through the center aperture 13 of inlet support member 3 and the flow area through the annular flange region 5 of the rupture disc 1.
It is therefore desirable to design an inlet support structure that will allow a tension acting rupture disc to rupture in such a fashion as to create a greater flow area through the rupture disc as compared to using a conventional inlet support structure as explained above.